Fructose Infusion Research Articles

Septal infusions of glucose or pyruvate, but not fructose, produce avoidance deficits when co-infused with the GABA agonist muscimol

Although glucose typically enhances memory or reverses memory deficits, glucose can also produce memory deficits when co-infused with the γ-aminobutyric acid (GABA) agonist muscimol into the medial septum ( Parent & Gold, 1997; Parent, Laurey, Wilkniss, & Gold, 1997). To date the mechanisms underlying the memory-impairing interaction between GABA and glucose remain unknown. Here we investigate whether this effect is the result of hyperosmolar conditions or may involve glucose metabolism. Male Sprague–Dawley rats were given one-trial inhibitory avoidance training after receiving septal infusions of vehicle (phosphate-buffered saline, 0.5 μl), the GABA A agonist muscimol (3 nmol), glucose (16.5, 33, or 66 nmol), fructose (33 nmol), pyruvate (33 nmol), or a solution containing muscimol combined with glucose, fructose, or pyruvate. Retention performance was tested 48 h later. Infusions of glucose, pyruvate, fructose, or muscimol alone did not affect retention performance. However, co-infusions of all doses of glucose (16.5, 33, or 66 nmol) or the glycolytic end product pyruvate with muscimol impaired retention performance. Co-infusions of fructose with muscimol did not affect retention performance. These results suggest that the memory-impairing interaction between glucose and muscimol does not result from hyperosmolar conditions, because equiosmolar concentrations of fructose do not mimic the effects of glucose and the memory deficits do not vary as a function of glucose concentration. The finding that pyruvate mimicked the effects of glucose and impaired memory when combined with muscimol suggests that glucose metabolism may be involved in the memory-impairing interaction between glucose and GABA A receptors in the medial septum.

Impact of chronic fructose infusion on hepatic metabolism during TPN administration.

During chronic total parenteral nutrition (TPN), net hepatic glucose uptake (NHGU) is markedly elevated. However, NHGU is reduced by the presence of an infection. We recently demonstrated that a small, acute (3-h) intraportal fructose infusion can correct the infection-induced impairment in NHGU. The aim of this study was to determine whether the addition of fructose to the TPN persistently enhances NHGU in the presence of an infection. TPN was infused continuously into the inferior vena cava of chronically catheterized dogs for 5 days. On day 3, a bacterial clot was implanted in the peritoneal cavity, and either saline (CON, n = 5) or fructose (+FRUC, 1.0 mg. kg(-1). min(-1), n = 6) infusion was included with the TPN. Forty-two hours after the infection was induced, hepatic glucose metabolism was assessed in conscious dogs with arteriovenous and tracer methods. Arterial plasma glucose concentration was lower with chronic fructose infusion (120 +/- 4 vs. 131 +/- 3 mg/dl, +FRUC vs. CON, P < 0.05); however, NHGU was not enhanced (2.2 +/- 0.5 vs. 2.8 +/- 0.4 mg. kg(-1). min(-1)). Acute removal of the fructose infusion dramatically decreased NHGU (2.2 +/- 0.5 to -0.2 +/- 0.5 mg. kg(-1). min(-1)), and net hepatic lactate release also fell (1.6 +/- 0.3 to 0.5 +/- 0.3 mg. kg(-1). min(-1)). This led to an increase in the arterial plasma glucose (Delta13 +/- 3 mg/dl, P < 0.05) and insulin (Delta5 +/- 2 micro U/ml) concentrations and to a decrease in glucagon (Delta-11 +/- 3 pg/ml) concentration. In conclusion, the addition of chronic fructose infusion to TPN during infection does not lead to a persistent augmentation of NHGU.

Fructose amplifies counterregulatory responses to hypoglycemia in humans.

Glucokinase (GK) is required for cellular glucose sensing, although there is a paucity of data regarding its role in the counterregulatory response to hypoglycemia in humans. Because fructose has been shown to modulate GK activity, we examined the effects of an acute infusion of fructose on hypoglycemia counterregulation in seven lean nondiabetic subjects. Using stepped hypoglycemia clamp studies (5.0, 4.4, 3.9, and 3.3 mmol/l target plasma glucose steps, 50 min each), subjects were studied on two separate occasions, without (control) or with co-infusion of fructose (1.2 mg.kg(-1).min(-1)). Fructose induced a resetting of the glycemic thresholds for secretion of epinephrine (3.8 +/- 0.1 mmol/l) and glucagon (3.9 +/- 0.2 mmol/l) to higher plasma glucose concentrations (4.0 +/- 0.1 mmol/l [P = 0.006] and 4.1 +/- 0.1 mmol/l [P = 0.03], respectively). In addition, the magnitude of increase in epinephrine and glucagon concentrations was higher after administration of fructose (48 and 39%, respectively, P < 0.05 for both). The amplification of these hormonal responses was specific because plasma norepinephrine, growth hormone, and cortisol were comparable in both sets of studies. Endogenous glucose production, measured with [3-(3)H]glucose, increased by 47% (P < 0.05) in the fructose infusion studies compared with 14% (P = NS) in the control studies. In addition, glucose uptake was more suppressed with fructose infusion (by 33%, P < 0.05). In concert with these effects of fructose on glucose kinetics, average glucose infusion rate was markedly reduced in the fructose infusion studies during the 3.9-mmol/l glucose step (4.6 +/- 0.9 vs. 7.4 +/- 1.1 micromol.kg(-1).min(-1), respectively, P = 0.03) and during the 3.3-mmol/l glucose step (0.5 +/- 0.1 vs. 5.2 +/- 1.2 micromol.kg(-1).min(-1), respectively, P < 0.001), suggesting more potent glucose counterregulation and improved recovery from hypoglycemia with fructose infusion. We conclude that infusion of a catalytic dose of fructose amplifies the counterregulatory response to hypoglycemia by both increases in hormonal activation and augmentation of glucose counterregulation in humans.

Fructose improves the ability of hyperglycemia per se to regulate glucose production in type 2 diabetes.

The ability of hyperglycemia per se to suppress endogenous glucose production (GP) is blunted in type 2 diabetes. This could be due in part to decreased glucose-induced flux through glucokinase (GK). Because fructose activates hepatic GK, we examined whether catalytic amounts of fructose could restore inhibition of GP by hyperglycemia in humans with type 2 diabetes. Glucose fluxes ([3-(3)H]glucose) were measured during euglycemia (5 mmol/l) and after abrupt onset of hyperglycemia (10 mmol/l; variable dextrose infusion) under fixed hormonal conditions (somatostatin infusion for 6 h with basal insulin/glucagon/growth hormone replacement). A total of 10 subjects with moderately controlled type 2 diabetes and 7 age- and BMI-matched nondiabetic subjects were studied on up to three separate occasions under the following conditions: without fructose (F(-)) or with infusion of fructose at two dosages: 0.6 mg/kg center dot min (low F) and 1.8 mg/kg center dot min (high F). Although GP failed to decrease in response to hyperglycemia in type 2 diabetes, the coinfusion of both doses of fructose was associated with comparable decreases in GP in response to hyperglycemia (low F = -27%, high F = -33%; P < 0.01 vs. F(-) at both dosages), which approached the 44% decline in GP observed without fructose in the nondiabetic subjects. GP responses to hyperglycemia were not altered by the addition of fructose in the nondiabetic group (low F = -47%, high F = -42%; P > 0.05 vs. F(-)). Thus, the administration of small amounts of fructose to type 2 diabetic subjects partially corrected the regulation of GP by hyperglycemia per se, yet did not affect this regulation in the nondiabetic subjects. This suggests that the liver's inability to respond to hyperglycemia in type 2 diabetes, likely caused by impaired GK activity, contributes substantially to the increased GP in these individuals.

Stimulating Effects of Low-Dose Fructose on Insulin-Stimulated Hepatic Glycogen Synthesis in Humans

Fructose has been shown to have a catalytic effect on glucokinase activity in vitro; however, its effects on hepatic glycogen metabolism in humans is unknown. To address this question, we used (13)C nuclear magnetic resonance (NMR) spectroscopy to noninvasively assess rates of hepatic glycogen synthesis and glycogenolysis under euglycemic (approximately 5 mmol/l) hyperinsulinemic conditions (approximately 400 pmol/l) with and without a low-dose infusion of fructose (approximately 3.5 micromol. kg(-1). min(-1)). Six healthy overnight-fasted subjects were infused for 4 h with somatostatin (0.1 micromol. kg(-1). min(-1)) and insulin (240 pmol. m(-2). min(-1)). During the initial 120 min, [1-(13)C]glucose was infused to assess glycogen synthase flux followed by an approximately 120-min infusion of unlabeled glucose to assess rates of glycogen phosphorylase flux. Acetaminophen was given to assess the percent contribution of the direct and indirect (gluconeogenic) pathways of glycogen synthesis by the (13)C enrichment of plasma UDP-glucuronide and C-1 of glucose. In the control studies, the flux through glycogen synthase and glycogen phosphorylase was 0.31 +/- 0.06 and 0.17 +/- 0.04 mmol/l per min, respectively, and the rate of net hepatic glycogen synthesis was 0.14 +/- 0.05 mmol/l per min. In the fructose studies, the glycogen synthase flux increased 2.5-fold to 0.79 +/- 0.16 mmol/l per min (P = 0.018 vs. control), whereas glycogen phosphorylase flux remained unchanged (0.24 +/- 0.06; P = 0.16 vs. control). The infusion of fructose resulted in a threefold increase in rates of net hepatic glycogen synthesis (0.54 +/- 0.12 mmol/l per min; P = 0.008 vs. control) without affecting the pathways of hepatic glycogen synthesis (direct pathway approximately 60% in both groups). We conclude that during euglycemic hyperinsulinemia, a low-dose fructose infusion causes a threefold increase in net hepatic glycogen synthesis exclusively through stimulation of glycogen synthase flux. Because net hepatic glycogen synthesis has been shown to be diminished in patients with poorly controlled type 1 and type 2 diabetes, stimulation of hepatic glycogen synthesis by this mechanism may be of potential therapeutic value.

Fructose augments infection-impaired net hepatic glucose uptake during TPN administration.

During chronic total parenteral nutrition (TPN), net hepatic glucose uptake (NHGU) and net hepatic lactate release (NHLR) are markedly reduced (downward arrow approximately 45 and approximately 65%, respectively) with infection. Because small quantities of fructose are known to augment hepatic glucose uptake and lactate release in normal fasted animals, the aim of this work was to determine whether acute fructose infusion with TPN could correct the impairments in NHGU and NHLR during infection. Chronically catheterized conscious dogs received TPN for 5 days via the inferior vena cava at a rate designed to match daily basal energy requirements. On the third day of TPN administration, a sterile (SHAM, n = 12) or Escherichia coli-containing (INF, n = 11) fibrin clot was implanted in the peritoneal cavity. Forty-two hours later, somatostatin was infused with intraportal replacement of insulin (12 +/- 2 vs. 24 +/- 2 microU/ml, SHAM vs. INF, respectively) and glucagon (24 +/- 4 vs. 92 +/- 5 pg/ml) to match concentrations previously observed in sham and infected animals. After a 120-min basal period, animals received either saline (Sham+S, n = 6; Inf+S, n = 6) or intraportal fructose (0.7 mg x kg(-1) x min(-1); Sham+F, n = 6; Inf+F, n = 5) infusion for 180 min. Isoglycemia of 120 mg/dl was maintained with a variable glucose infusion. Combined tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism. Acute fructose infusion with TPN augmented NHGU by 2.9 +/- 0.4 and 2.5 +/- 0.3 mg x kg(-1) x min(-1) in Sham+F and Inf+F, respectively. The majority of liver glucose uptake was stored as glycogen, and NHLR did not increase substantially. Therefore, despite an infection-induced impairment in NHGU and different hormonal environments, small amounts of fructose enhanced NHGU similarly in sham and infected animals. Glycogen storage, not lactate release, was the preferential fate of the fructose-induced increase in hepatic glucose disposal in animals adapted to TPN.

Thermogenesis induced by osmotic stimulation of the intestines in the rat.

Infusion of 5-20% glucose, 1.8-3.6% NaCl, 20% methylglucose, 20% fructose, or 5-10% solutions of various amino acids (10 ml x kg(-1)) into the duodenum induced dose-dependent thermogenesis in urethane-anaesthetized rats. In contrast, infusion of 0.9% NaCl, distilled water, or safflower oil had no effect on the metabolic rate. Infusion of 7.2% urea induced a small and transient increase in the metabolic rate. These results suggested that the thermogenesis was caused mainly by changes in osmolality rather than by a specific action of the different solute molecules. The respiratory exchange ratio increased after the infusion of glucose, fructose, glycine, or serine, did not change after the infusion of NaCl, methylglucose, safflower oil, or distilled water, and decreased after infusion of arginine. Therefore, there was no relationship between substrate utilization and the occurrence of thermogenesis. Intestinal infusion of 3.6% NaCl elevated the plasma osmolality, with a plateau increase of approximately 20 mosmol x kg(-1). However, intravenous infusion of the same amount of NaCl induced a significantly smaller thermogenic response, although it elevated the plasma osmolality with a time course and magnitude similar to those obtained after the intestinal infusion. Infusion of NaCl into the hepatic portal vein or the peritoneal cavity also produced a significantly small thermogenic response. These results suggested an intestinal or mesenteric location for osmoreceptors. To test for possible stimulation of intestinal osmoreceptors after intake of a normal meal, we measured the osmolality of the intestinal contents. The osmolality of the duodeno-jejunal contents was 600-800 mosmol kg-1, whereas the plasma osmolality was 306 +/- 1 mosmol x kg(-1), which suggests that the intestinal osmoreceptors are stimulated after meals and are involved in diet-induced thermogenesis.

Hepatic intralobular mapping of fructose metabolism in the rat liver

Detailed mapping of glucose and lactate metabolism along the radius of the hepatic lobule was performed in situ in rat livers perfused with 1.5 mM lactate before and during the addition of 5 mM fructose. The majority of fructose uptake occurred in the periportal region; 45% of fructose taken up in the periportal half of the lobular volume being converted into glucose. Periportal lactate uptake was markedly decreased by addition of fructose. Basal perivenous lactate output, which was derived from glucose synthesized periportally, was increased in the presence of fructose. During fructose infusion there was a small decrease in cell pH periportally, but acidification of up to 0.5 pH units perivenously. The evidence suggests that in situ the apparent direct conversion of fructose into lactate represents, to a substantial extent, the result of periportal conversion of fructose into glucose and the subsequent uptake and glycolysis to lactate in the perivenous zone of some of that glucose. 31P NMR spectroscopy showed that the cellular concentration of phosphomonoesters changes very little periportally during fructose infusion, but there was an approximate twofold increase perivenously, presumably due to the accumulation of fructose 1-phosphate. It may be inferred that fructokinase activity is expressed throughout the hepatic lobule.

Hepatic intralobular mapping of fructose metabolism in the rat liver.

Detailed mapping of glucose and lactate metabolism along the radius of the hepatic lobule was performed in situ in rat livers perfused with 1.5 mM lactate before and during the addition of 5 mM fructose. The majority of fructose uptake occurred in the periportal region; 45% of fructose taken up in the periportal half of the lobular volume being converted into glucose. Periportal lactate uptake was markedly decreased by addition of fructose. Basal perivenous lactate output, which was derived from glucose synthesized periportally, was increased in the presence of fructose. During fructose infusion there was a small decrease in cell pH periportally, but acidification of up to 0.5 pH units perivenously. The evidence suggests that in situ the apparent direct conversion of fructose into lactate represents, to a substantial extent, the result of periportal conversion of fructose into glucose and the subsequent uptake and glycolysis to lactate in the perivenous zone of some of that glucose. (31)P NMR spectroscopy showed that the cellular concentration of phosphomonoesters changes very little periportally during fructose infusion, but there was an approximate twofold increase perivenously, presumably due to the accumulation of fructose 1-phosphate. It may be inferred that fructokinase activity is expressed throughout the hepatic lobule.

Alterations in liver ATP homeostasis in human nonalcoholic steatohepatitis: a pilot study.

The mechanisms that drive progression from fatty liver to steatohepatitis and cirrhosis are unknown. In animal models, obese mice with fatty livers are vulnerable to liver adenosine triphosphate (ATP) depletion and necrosis, suggesting that altered hepatic energy homeostasis may be involved. To determine if patients with fatty liver disease exhibit impaired recovery from hepatic ATP depletion. Laboratory analysis of liver ATP stores monitored by nuclear magnetic resonance spectroscopy before and after transient hepatic ATP depletion was induced by fructose injection. The study was conducted between July 15 and August 30, 1998. University hospital. Eight consecutive adults with biopsy-proven nonalcoholic steatohepatitis and 7 healthy age- and sex-matched controls. Level of ATP 1 hour after fructose infusion in patients vs controls. In patients, serum aminotransferase levels were increased (P = .02 vs controls); albumin and bilirubin values were normal and clinical evidence of portal hypertension was absent in both groups. However, 2 patients had moderate fibrosis and 1 had cirrhosis on liver biopsy. Mean serum glucose, cholesterol, and triglyceride levels were similar between groups but patients weighed significantly more than controls (P = .02). Liver ATP levels were similar in the 2 groups before fructose infusion and decreased similarly in both after fructose infusion (P = .01 vs initial ATP levels). However, controls replenished their hepatic ATP stores during the 1-hour follow-up period (P<.02 vs minimum ATP) but patients did not. Hence, patients' hepatic ATP levels were lower than those of controls at the end of the study (P = .04). Body mass index (BMI) correlated inversely with ATP recovery, even in controls (R = -0.768; P = .07). Although BMI was greater in patients than controls (P = .02) and correlated strongly with fatty liver and serum aminotransferase elevations, neither of the latter 2 parameters nor the histologic severity of fibrosis strongly predicted hepatic ATP recovery. These data suggest that recovery from hepatic ATP depletion becomes progressively less efficient as body mass increases in healthy controls and is severely impaired in patients with obesity-related nonalcoholic steatohepatitis.

Changes in Fructose-Induced Production of Glucose in the Rat Liver Following Partial Hepatectomy

The fructose-induced production of glucose in the liver after partial hepatectomy (PH) was evaluated by using the liver-perfusion system. There was no significant difference in plasma glucose level between hepatectomized (HX) and sham-operated (SO) rats at 24 h after surgery, and, thereafter, almost similar levels were obtained in both groups. However, the level of serum free fatty acids (FFA) was significantly higher in HX rats than that in SO rats at 24 and 48 h after surgery. When both groups of rats were given fructose by gavage, the increment of plasma glucose was significantly larger in HX rats than in SO rats. Lactate infusion failed to increase the rate of glucose production in perfused livers of both HX and SO rats and there was no significant difference in the activity of hepatic phosphoenolpyruvate carboxykinase. By contrast, fructose infusion elicited a large increase in glucose production in the perfused livers of HX rats at 24 and 48 h after PH. The increase was closely associated with not the change in fructose 2,6-bisphosphate levels but the increment of the intracellular levels of citrate. Treatment of octanoate or oleate, which supplies acetyl-CoA via fatty acid oxidation, mimicked the fructose-induced increase in glucose production in SO rats with a concomitant increase in hepatic levels of citrate. These results suggest that the oxidation of FFA may play an important role in glucose production induced by fructose administration during the early phase of liver regeneration.

Conditioned Flavor Avoidance, Preference, and Indifference Produced by Intragastric Infusions of Galactose, Glucose, and Fructose in Rats

SCLAFANI A., L. J. FANIZZA AND A. V. AZZARA. Conditioned flavor avoidance, preference, and indifference produced by intragastric infusion of galactose, glucose, and fructose in rats. PHYSIOL BEHAV 67(2) 227–234, 1999.—The postingestive reinforcing and satiating effects of intragastric (i.g.) infusions of 16% galactose, glucose, and fructose were compared in adult female rats. In Experiment 1, food-restricted rats were trained to drink (30 min/day) flavored solutions (the CS+Gal and CS+Glu) paired with intragastric (i.g.) infusions of galactose and glucose; other flavors (the CS−) were paired with IG water infusions. In subsequent choice tests, the rats strongly preferred (91%) the CS+Glu to the CS−, but avoided the CS+Gal (21%) in favor of the CS−. In Experiment 2, the rats were trained with a CS+Fru paired with i.g. fructose infusions and a CS− paired with i.g. water. In the choice test they consumed similar amounts of CS+Fru and CS− (CS+Fru preference = 51%). In other choice tests they preferred the CS+Glu (>80%) to CS+Fru and CS+Gal, and the CS+Fru (81%) to CS+Gal. Satiation tests were performed in Experiment 3 by adapting the rats to drink a 3% sugar + 0.2% saccharin solution paired with i.g. water infusions (30 min/day). On different test days 16% sugar instead of water was infused. IG galactose, glucose, and fructose produced comparable reductions in sugar+saccharin intake in the first test session. These findings demonstrate that, while the three sugars had similar satiating effects, they differed substantially in their postingestive flavor conditioning effects. The glucose and fructose results confirm prior data indicating that only glucose generates potent postingestive reinforcing stimuli. The galactose-induced flavor avoidance indicates that this sugar has a negative postingestive consequence. This may be due to the slow and incomplete hepatic metabolism of this sugar in adult rats. Conceivably, galactose intolerance may contribute to the lactose avoidance in adult animals.

Effects of glucagon in the control of endogenous glucose production in man.

Endogenous glucose production has been shown to increase during administration of glucagon + fructose, but not during administration of fructose alone. To determine the mechanisms by which glucagon exerts this action, endogenous glucose production (EGP) and gluconeogenesis from fructose (GNF) were measured in eight healthy subjects infused 1) with graded doses of glucagon (2 and 4 ng.kg-1.min-1 for 3 h each) during constant infusion of 13C-fructose (3 mg.kg-1.min-1), and 2) with graded doses of 13C-fructose (3 and 6 mg.kg-1.min-1) during constant glucagon infusion (2 ng.kg-1.min-1). GNF was estimated from 13C-glucose synthesis. In both protocols, infusion of 3 mg.kg-1.min-1 fructose + 2 ng.kg-1.min-1 glucagon increased EGP by 5-8% (P < 0.05), while GNF represented 43-49% of EGP. Thereafter, increasing the glucagon infusion rate further increased EGP to 118 +/- 3% of basal values (P < 0.01) without altering the proportion due to GNF. In contrast, increasing the fructose infusion rate at constant glucagonemia increased EGP similarly (by 19 +/- 4%, P < 0.05) but enhanced the contribution of GNF to 76 +/- 2% (P < 0.001). Graded infusion of glucagon or fructose alone failed to stimulate EGP. The present findings indicate that hyperglucagonemia stimulates endogenous glucose production during fructose infusion. This effect is not secondary to a stimulation of gluconeogenesis, but to a channelling of glucose-6-phosphate towards systemic release.

Determination of adenosine and deoxyadenosine in urine by high-performance liquid chromatography with column switching

The means of measurement of adenosine and deoxyadenosine in urine was developed by separating adenosine and deoxyadenosine from other compounds using high-performance liquid chromatography with column switchings. This method is simple and convenient since no pretreatment of the urine is needed. Using this method, it could be demonstrated that urinary adenosine was higher in an adenosine deaminase (ADA) deficient patient who had a bone marrow transplant treatment (1.97 μmol/mmol creatinine) and in a heterozygote who had a markedly low erythrocyte ADA activity (1% of control ADA activity) (1.33 μmol/mmol creatinine) as compared to normal subjects (0.22±0.09 μmol/mmol creatinine, n=11). It was also noted that urinary deoxyadenosine was below the detection limits in the ADA-deficient bone marrow transplant patient, but it was detected in the heterozygote (3.7 μmol/mmol creatinine). Furthermore, it was also demonstrated that a fructose infusion increased the urinary concentration of adenosine from 0.21±0.03 to 2.66±1.21 μmol/mmol creatinine in five normal subjects.

Simple, Rapid Nonradioactive Method to Detect the Three Most Prevalent Hereditary Fructose Intolerance Mutations

Hereditary fructose intolerance (HFI) is an autosomal recessive disorder, the true incidence of which is not known but may be estimated as high as 1 of 20 000 (1)(2). It is caused by any of several molecular abnormalities of the human aldolase B gene (3). Twenty-one mutations have been reported worldwide (2). Three mutations (A149P, A174D, and N334K) of the aldolase B gene account for 95% of the defective alleles in Europe (2 , 4) . They are investigated by various methods, including restriction enzyme digestion, direct sequencing, use of an amplification refractory mutation system, and allele-specific oligonucleotide hybridization (4). Unidentified HFI patients are at high risk if inadvertently given an infusion of fructose, sorbitol, or inverted sugar (5)(6). Three methods are used for diagnosis. The measurement of blood variables in response to intravenous fructose tolerance test and assay for aldolase B activity on liver biopsy samples are both invasive methods and do not allow heterozygote diagnosis (7). The third method, allele-specific oligonucleotide hybridization (4), circumvents these issues but is a radiobioassay restricted to certified laboratories. We have developed a simple and rapid method for detecting simultaneously the three most prevalent mutations in Europe by PCR-mediated, site-directed mutagenesis and restriction analysis. We investigated the diagnostic value of this method in patients from independent families. Thirty-five HFI patients from 30 independent families were studied. HFI presented with acute symptoms (hypoglycemia, vomiting, and liver failure) before 6 months of age in 12 patients. In a second group of 23 patients, HFI presented with symptoms related to chronic exposure (hepatomegaly, growth delay, and aversion toward foods containing fructose) between 1 and 6 years of age. Diagnosis was assayed by conventional methods: intravenous fructose tolerance tests or aldolase B activity assays in liver biopsy samples. Genomic DNA was obtained from …

Spontaneous pregnancy toxaemia (ketosis) in sheep and the role of insulin.

214 ewes suffering from pregnancy toxaemia (ketosis) were examined. Clinical signs during onset and course of disease and laboratory findings were compared between animals that survived and those which died. In the latter the onset of ketosis was earlier in pregnancy (day 143 +/- 7 vs. day 146 +/- 8) and duration of the disease was shorter (10 +/- 13 vs. 14 +/- 9 days). The animals that died showed more severe clinical signs and higher values of 3-hydroxy-butyrate (4.3 +/- 3.6 vs. 3.5 +/- 2.6 mmol/l) and cortisol (72 +/- 98 vs. 52 +/- 80 mmol/l) as well as lower values of insulin (37 + 12 vs. 3.5 + 2.6 mmol/l) and potassium (4.1 + 1.0 vs. 4.4 + 1.0 mmol/1) at onset of the disease than those which survived (all of differences with P < 0.05). Glucose levels did not differ between groups. Treated animals with glucose plus fructose infusions (n = 56) or with oral application of glucose precursors plus electrolytes (n = 126) had survival rates of 53.6% and 62.7%, respectively. Oral treatment with glucose precursors plus electrolytes and an additional subcutaneous insulin treatment (n = 15) led to an enhanced survival rate of 86.7% (P < 0.05). Low insulin levels in ketotic pregnant sheep and the therapeutic effect of insulin treatment support the hypothesis that insulin plays a causative role in the pathogenesis of ovine ketosis.

Effect of ethanol and fructose on plasma uridine and purine bases

To determine whether both ethanol and fructose increase the plasma concentration of uridine, we administered ethanol (0.6 g/kg) or fructose (1.0 g/kg) to seven normal subjects. Both ethanol and fructose increased the plasma concentration of uridine together with an increase in the plasma concentration of oxypurines, whereas fructose also increased the plasma concentration of uric acid, but ethanol did not. In ethanol ingestion and fructose infusion, an increase in the plasma concentration of purine bases correlated with that of uridine. These results strongly suggest that an increase in the plasma concentration of uridine is ascribable to increased pyrimidine degradation following purine degradation increased by ethanol and fructose.

Diabetic Rats Prefer Glucose-paired Flavors over Fructose-paired Flavors

Prior studies indicate that glucose has a more potent postingestive reinforcing effect than fructose. The role of insulin in this effect was examined by comparing sugar-conditioned flavor preferences in normal and streptozotocin-diabetic rats. In Experiment 1, diabetic rats, like normal rats, preferred a cue flavor that had been mixed into 8% glucose solution over a flavor mixed with 8% fructose. Both taste and postingestive properties of glucose may have contributed to this preference. Experiment 2 evaluated postingestive reinforcement by pairing cue flavors with intragastric infusions of glucose and fructose. Both diabetics and normals acquired a preference for the flavor paired with intragastric 16% glucose infusions over the flavor paired with 16% fructose infusions although the preference was somewhat smaller in the diabetic rats. Taken together, the results indicate that a normal insulin secretory response to glucose is not required for glucose-conditioned flavor preferences. The diabetic rats' reduced flavor preference in Experiment 2 suggests that insulin may play some role in glucose conditioning although this may be secondary to alterations in gastrointestinal motility characteristic of diabetic animals.

Food intake and diet selection in sheep: the effect of manipulating the rates of digestion of carbohydrates and protein of the foods offered as a choice.

An experiment was designed to investigate whether the degree of synchrony between the rates of digestion of carbohydrates and N of foods offered as a choice would have an effect, through their consequences, on the short- and long-term diet selection of sheep. Four foods (RL, RH, SL and SH) with the same high metabolizable energy, and similar high metabolizable protein contents were made into pellets. Foods RL and RH were based on a rapidly fermentable carbohydrate source and foods SL and SH on a slowly fermentable carbohydrate source; within each source one food (RL or SL) had a low, and the other (RH or SH) a high, rumen-degradable protein (RDP) content. The foods within a carbohydrate source were offered either singly or as a choice (RL/RH or SL/SH) to eleven rumen-fistulated mature sheep. The design was two 3 x 3 Latin squares (replicated once) with 5-week periods; squares consisted of two single foods and their respective choice. Weeks 1, 3 and 5 were considered to be controls, and weeks 2 and 4 used for rumen infusions of either urea or fructose infused over 4 h (10.00-14.00 hours). Food intake (FI) and diet selections (DS) were recorded daily and every 2 h (08.00-16.00 hours) on days 2-5 of each week; rumen pH and NH3 concentrations were also measured during these time intervals of day 5. As expected, feeding treatment affected significantly the rumen measurements: rumen NH3 concentrations were higher on foods RH and SH, and rumen pH lowest on RL. Daily FI was lowest on treatments SL, and choice SL/SH. The mean daily proportion of the low-RDP food in the selected diet was lower when the carbohydrate source was rapidly (choice RL/RH) rather than slowly fermentable (choice SL/SH); this was consistent with the experimental hypothesis. Short-term infusions affected further rumen variables (in the expected directions), irrespective of feeding treatment. However, DS over the 4h infusion period were unaffected; these short-term DS were consistent with the ones selected over the longer term (daily). The results suggest that the long-term (daily) diet selection of sheep may be affected by the degree of synchrony of energy and protein to the rumen. The fact that diet selections were not altered further by short-term manipulations of these supplies might reflect inadequacies of the methodology (infusions) adopted here.

Early detection of cancer cachexia in the rat using 31P magnetic resonance spectroscopy of the liver and a fructose stress test.

The dynamic metabolic effects of a fructose infusion challenge on hepatic intracellular levels of adenosine 5'-triphosphate (ATP), inorganic phosphate (Pi) and phosphomonoesters (PME) were monitored noninvasively by 31P MRS in a remote tumour-bearing rat model. Fisher male rats were inoculated with a methylcholanthrene-induced sarcoma. Seventeen rats were randomized into three groups: control (n = 6), low tumour burden (LTB, n = 6), or moderate tumour burden (MTB, n = 5). The LTB group had tumour burdens of 0.2-2.0% while the MTB group had tumour burdens of 2.6-5.7%. All rats were in the pre-clinical phase of cancer cachexia as determined by food intake and body weight. Rats were infused with 1.2 g/kg of fructose i.v. and the metabolic response of the liver was monitored with time over 1 h via 31P MRS. In all groups an immediate increase in hepatic levels of PME was noted, which returned to baseline values over the course of the experiment, reflecting the phosphorylation of fructose to fructose 1-phosphate. For the MTB rats, the return to baseline levels was more rapid than in the control or LTB group. All groups experienced a 20% decrease in hepatic ATP levels which did not return to baseline over the 1 h observation period. As well, all groups experienced an initial fall in Pi, which recovered to prefructose levels or greater. MTB rats demonstrated a 30-40% increase in Pi concentration and a 60-70% increase in Pi/ATP ratio after infusion with fructose as compared to LTB and control rats (ANOVA;p<0.05). This is consistent with cachexia-induced enhancement of hepatic gluconeogenic activity, and hence more rapid release of Pi from the phosphorylated metabolites in the MTB rats. Thus fructose infusion and hepatic 31P MRS permit pre-clinical detection of cancer cachexia as reflected by increased Pi generation and more rapid removal of PME.